Question: Solve for $x$ and $y$ using substitution. ${-3x-3y = -12}$ ${x = -2y+3}$
Explanation: Since $x$ has already been solved for, substitute $-2y+3$ for $x$ in the first equation. ${-3}{(-2y+3)}{- 3y = -12}$ Simplify and solve for $y$ $6y-9 - 3y = -12$ $3y-9 = -12$ $3y-9{+9} = -12{+9}$ $3y = -3$ $\dfrac{3y}{{3}} = \dfrac{-3}{{3}}$ ${y = -1}$ Now that you know ${y = -1}$ , plug it back into $\thinspace {x = -2y+3}\thinspace$ to find $x$ ${x = -2}{(-1)}{ + 3}$ $x = 2 + 3$ ${x = 5}$ You can also plug ${y = -1}$ into $\thinspace {-3x-3y = -12}\thinspace$ and get the same answer for $x$ : ${-3x - 3}{(-1)}{= -12}$ ${x = 5}$